An oriented silicon steel has been widely applied to power transmission and transformation products such as large-scale transformers, and becomes one of indispensible raw materials in development of power industry. At present, people are committed to obtaining an oriented silicon steel with excellent magnetic properties. The main technical indexes of the magnetic properties in the oriented silicon steel comprise magnetic induction and iron loss, and the iron loss is directly related to the loss of an iron core when using power transmission and transformation products such as a transformer. It is said that the development history of silicon steel products is the history that the iron loss is continuously reduced actually. The magnetic induction, namely magnetic induction intensity, also known as magnetic flux density, reflects the magnetization intensity of a ferromagnetic material in a magnetic field, and the changes in the value of the magnetic induction per unit of magnetic field intensity is represented by magnetic conductivity. Under the using conditions of a user, the properties of the silicon steel product are closely related to the intensity of an external magnetic field, so that the magnetic conductivity, especially the magnetic conductivity in the vicinity of a working point of the transformer and other products, is more suitable for representing the magnetic properties under a certain magnetic field intensity. According to the investigation, in the related prior documents of the oriented silicon steel, the studies which are directly related to magnetic properties such as the magnetic conductivity are very few, and the studies regarding the influence of the structure of the oriented silicon steel material on key properties such as the magnetic conductivity are even fewer.
Japanese Patent JP 60-59045A and Chinese Patent CN 91103357 respectively disclose that, by adopting a cold rolling aging rolling method, the number of small crystal grains with grain equivalent circle diameter D of not more than 2 mm in an oriented silicon steel finished product can be increased, so that the iron loss of the oriented silicon steel finished product can be reduced. But in the above patent literatures, only on the premise that the secondary recrystallization of the oriented silicon steel finished product is perfect, appropriately increasing the number of the small crystal grains contributes to decrease the iron loss. And, the small crystal grains herein should be specifically understood to be small-size grains with relatively small deviation angles with the direction of a Goss texture, namely (110)[001] direction, otherwise, the effect of improving the magnetic properties is difficult to achieve. Thus, the way of only increasing the number of the small crystal grains in the oriented silicon steel finished product should not become the standard of judging whether the magnetic properties of the oriented silicon steel are improved, this is because that the grain orientation of the small-size grains is highly possible to be subjected to large-angle deviation from the direction of the Goss texture, the possibility is far higher than that of large-size grains, and the appearance of a large number of small crystal grains having a large-angle deviation from the Goss texture will seriously degrade the magnetic properties of the oriented silicon steel finished product. On the contrary, the average deviation angle between the orientation of the large crystal grains with the grain equivalent circle diameter D of not less than 5 mm and the Goss texture generally is within 7°. Thus, under general circumstances, by increasing the number or the area ratio of the large crystal grains in the oriented silicon steel finished product or controlling the number or the area ratio of the small crystal grains to be within a certain range, it can be better ensured that the oriented silicon steel has good magnetic properties and the stability in the magnetic properties.
In U.S. Pat. No. 7,887,645B1, it is mentioned that by controlling the ratio of an Austenite phase in an oriented silicon steel hot rolled plate, the normalization cooling rate is increased, and the magnetic conductivity can be improved. But in this patent, the ‘magnetic conductivity’ specifically refers to the magnetic induction under the magnetic field intensity of 796 A/m and is not the magnetic conductivity defined in general physical meaning. Furthermore, a large amount of Cr is added in a slab of the patent, thereby being adverse to environmental friendliness and being also adverse to stably obtaining the oriented silicon steel product with high magnetic properties. In addition, in the patent, it is recommended to heat the slab at the high temperature of about 1400° C., so that a special heating furnace needs to be configured, and the energy consumption is relatively high; and furthermore, molten slag appears on the surface of the steel slab, the heating equipment needs to be cleaned regularly, the yield is affected, the finished product rate is reduced, the maintenance cost of the equipment is high, and thus the patent is not suitable for popularization.
In U.S. Pat. No. 5,718,775A, it is mentioned that the magnetic conductivity of the oriented silicon steel finished product under the magnetic induction of 1.0 T needs to be controlled to be not lower than 0.03 H/m. However, according to the actual technical magnetization hysteresis loop analysis, under the relatively low magnetic field, when the magnetic induction is relatively low, domain walls of magnetic domains move; and with the increase of the magnetic field intensity, the magnetic induction is increased, and when the magnetic induction is about 1.5-1.9 T, the magnetic domains which have grown due to the movement of the domain walls and the magnetic domains which have not been swallowed up occur irreversible rotation so as to enable magnetization vectors to be parallel to the direction of the magnetic field gradually. The process is continued till the magnetization vectors of all the magnetic domains are rotated to be parallel to the direction of the magnetic field, and at this time, a saturated magnetic induction value Bs of the material is achieved. Working points used in products such as the transformer are generally designed to be within the magnetic induction range of 1.5-1.7 T, so that the control requirements for the magnetic conductivity of the oriented silicon steel under the magnetic induction of 1.0 T in U.S. Pat. No. 5,718,775A do not have practical significance.
Although some development have been made in the aspects of improving the magnetic conductivity and the iron loss of the oriented silicon steel in the prior art, there is still large room in the aspects of improving the magnetic properties of the oriented silicon steel under the working magnetic flux density of 1.5-1.7 T. People hopes to develop the oriented silicon steel with excellent magnetic properties under the working magnetic flux density of 1.5-1.7 T to satisfy the requirements of electronic equipments such as the transformer. In addition, the conventional manufacturing method of the oriented silicon steel still has the relatively large improvement room, and the research and development of the manufacturing method capable of obtaining the oriented silicon steel with excellent magnetic properties also has important significance and broad application prospects.